Effect of annealing temperature on thermoelectric properties of YBa2Cu3O7-x ceramic

We have studied the effect of annealing temperature on oxygen content and thermoelectric properties of YBa2Cu3O7-x (YBCO) ceramics fabricated by hot-pressing method. The as-calcined powder was subjected to the applied pressure of 70 MPa at 800 °C for 1 h under Ar atmosphere. The YBCO ceramics were then annealed at 700 and 750 °C for 4 h in oxygen atmosphere. The XRD results showed that all samples possessed pure orthorhombic YBCO phase. The annealing process seemed to induce the reduction of the electrical conductivity and metallic-to-semiconducting transition when the annealing temperature was increased. The temperature dependence of ZT showed a close relation to that of electrical conductivity, suggesting the dominant role of the charged carriers present in these samples.